Influence of additives on sodium release and ash sintering temperature of a high-alkali coal

The influence of three additves (Kaolin, SiO₂ and Al₂O₃) on sodium release and ash sintering temperature of high-alkali Zhundong coal with addition ratio range of 1%-5% was studied. The results indicate that the order of sodium capture efficiency for the additives is:Kaolin > SiO₂ > Al₂O₃. The sodium capture efficiency increases with the addition ratio. However, the effect of temperature is much complex. At 600-1000℃, the sodium caputre efficiency of Kaolin increases firstly and then decreases, and the maximum value is achieved at 900℃. Meanwhile, the sodium capture efficiencies of other two additives decrease with increasing temperature. In addition, the ash sintering temperature of Zhundong coal is 803℃. After adding Kaolin, it decreases firstly and then increases with the addition ratio. At the addition ratio of 3%, the sintering tempeature is lowest due to the low-melting eutectic reaction between gehlenite and anorthite. SiO₂ with 5% can increase the sinntering temperature to 879℃ sharply because of generation of diopside and its skeleton effect. The influence of Al₂O₃ on the sintering temperature is minimal.